In many countries, new injecting drug users (IDUs) are at substantial risk of becoming infected with HIV and hepatitis C (HCV). New IDUs are at increased risk of infection if their risk networks (i.e., the people with whom they use drugs or have sex) and social influence networks (i.e., the people with whom they interact and who influence their behavior) are high risk. Understanding how network and behavioral risks for infection among new injectors vary cross-nationally is essential to the development of international and local public health policies and preventive interventions to combat the AIDS and HCV epidemic among IDUs. Comparative studies of new IDUs in different countries can contribute to an understanding of how cross-national differences in the social and drug using environment and cultural contexts can influence the network and behavioral risks of new IDUs. This proposal is submitted to obtain a R03 grant for exploratory international research that will involve a collaboration between Dr. Alan Neaigus of the National Development and Research Institutes, in New York City, and Dr. Anne Lovell of the National Institute of Health and Medical Research (INSERM), U 379, in Marseilles, France. The purpose of the research is to examine network and behavioral risks for HIV and HCV infection among new IDUs (those who started to inject drugs within the last 6 years and who are from 18 to 30 years of age). The study will conduct preliminary analyses of survey and HIV and HCV test data from ongoing studies of IDUs in New York and Marseilles to compare the network and behavioral risks of new IDUs in the two cities. Qualitative research using institutional and ethnographic data will also be conducted to explore the extent to which differences in the drug use and social benefit environments affect new injectors' network and behavioral risk. Since there are many IDUs of North African origin in Marseilles, the study will also conduct exploratory research to understand whether transnational travel patterns between Southern France and North Africa by IDUs of North African origin are related to their network and behavioral risks for HIV and HCV. Findings from the preliminary analyses of the survey and biological data and from the exploratory qualitative research will be used to generate hypotheses and to develop the conception and design of a future larger scale study of new injectors in the two cities that will be submitted as an RO1 application.